Striatal neurons are involved in controlling movement and also in mediating reward, motivation and social behavior. At the level of the nucleus the differentiation of progenitors into different striatal neuronal phenotypes that mediate striatal functions is regulated by transcription factors. Currently, the coordinated and cooperative interactions of transcription factors required for normal striatal development is not well understood. A combination of Western-analysis, RT-PCR, immunohistochemistry and electrophoretic mobility shift assays (EMSA) demonstrated that the lymphoid zinc-finger transcription factor Ikaros, which controls T- and B-cell differentiation is specifically expressed in the developing striatum. A transient transfection assay in differentiating striatal neurons indicated that Ikaros activity is required for the developmental expression of the enkephalin (ENK) gene that encodes one of the most abundant striatal peptide neurotransmitters. The hypothesis of this application is that Ikaros regulates striatal differentiation by regulating the entry of progenitors into the differentiation pathway. The objective of this application is to map Ikaros expression in the developing striatum and to analyze the effect of its altered availability on striatal differentiation. The spatiotemporal pattern of Ikaros expression will be determined at various stages of striatal differentiation in the rat. Ikaros positive cells will be analyzed for proliferation (BrdU incorporation) and for the expression of selected developmental and phenotypic markers, including nestin, MAP2, NF68, ENK, substanceP/Neurokinin, dynorphin, D1 and D2 dopamine receptors, calbindin D-28 and DARRP-32 by immunohistochemistry and by in situ hybridization histochemistry. This information will provide information about the spatiotemporal distribution, developmental status and phenotype of Ikaros expressing cells. The availability of Ikaros will be altered by antisense oligonucleotide treatment or by overexpression in embryonic striatal cultures at various stages of differentiation. Following treatments changes in the expression of markers listed above and the number of apoptotic (TUNEL+) cells will be determined by immunohistochemistry, in situ hybridization histochemistry and TUNEL assay. These experiments will provide information about the role of Ikaros in striatal development. The proposed experiments will help to design future in vivo studies using animal models and in vitro studies focussing on the role of Ikaros in chromatin remodeling implicated in the development lymphoid system. Our studies will advance our knowledge about the molecular requirements for normal striatal development and contribute to a better understanding of developmental brain disorders.